Minimize OLCI Level 1 Processing - Earth Observation

Four auxiliary files are read during OLCI Level-1 processing in Earth Observation mode:

  • The OLCI Level-1 Classification Thresholds LUTs data file contains the LUTs of thresholds enabling derivation of bright pixel and sun glint risk flags, depending on the sun and viewing geometries, the sun zenith angle and the amplitude of the wind at pixel. The bright test LUT contains thresholds for direct comparison with the reflectance at pixel. The sun glint risk LUT is expressed as a wave angle characterising the scattering angle around the specular direction.
  • The OLCI Level-1 Characterisation and Models data file contains data acquired during the on-ground instrument characterisation campaign, as well as reference values inherent to the instrument. This file is divided into several groups, described in Table 1.
  • The OLCI Level-1 Calibration data file contains data updated during the life of the satellite relating to the calibration coefficients and parameters computed through the calibration processing. These data are described in Table 2 and categorised into groups.
  • The OLCI Level-1 Programmation data file contains data related to the instrument programmation. These data are described in Table 3 and categorised into groups.
Table 1: Groups of the OLCI Level-1 Characterisation and Models data file
Groups Description
transmission Gathering the overall transmissions of the main optical components of each module (i.e. the imaging sub-assembly comprising the ground imager, scrambling window and spectrometer), as well as their uniformity within its field of view.
CCD spectral responsivity Giving the per-channel average spectral responsivity of the CCD detector.
CCD offset compensation Containing the coefficients of the linear relation, linking the correction factor to be applied to the dark current of the instrument (at nominal CCD temperature) to the per-module CCD temperature variation along the orbit.
gain values Describing all electronic gains of the detection chain of each module of the instrument.
white diffuser geometry Providing the observation angles under which the white diffusers (nominal and ageing calibration) are viewed by each pixel. This group also gives the normal vectors for each of these diffusers.
white diffuser ageing model Gathering all parameters (reference time, polynom degree and polynom coefficients for each white diffuser) of the polynom describing the ageing model of each of the white diffusers.
white diffuser BRDF model Giving all parameters necessary to entirely define the BRDF models to be used for the nominal diffuser and the one dedicated to ageing calibration.
pink diffuser BRDF model Giving the relative spectral BRDF spectrum to be used as a reference for spectral calibration processing.
non linearity LUT inverse Corresponding to the LUT enabling correction of the count from the overall instrument non-linearity, given at micro-band level for each of the eight programmable gains.
pixel pointing vectors IF Providing the (x,y) components in the instrument frame of the OLCI pointing unit vectors for each pixel of each module. It is given at one reference wavelength which is also identified in this group.
quantity Gathering all parameters linked to instrument design (e.g. number of bands, micro-bands, CCD lines in total and dedicated to the smear band, dark and blank pixels).
band definition Providing the nominal definition of OLCI bands.
nadir along track SSD Giving the distance on the ellipsoid between two successive frames and the corresponding angle as viewed from the satellite.
nominal temperature Providing the nominal temperatures, in particular that of the CCD to be used in computation of a corrective factor to be applied to the instrument offset to correct for CCD temperature during data calibration.
time parameters Gathering all reference time parameters linked to OLCI design, in particular the offset between ISP time and real time at mid-exposure of the CCD.
calibration mechanism Containing the references for calibration mechanism targets, names and angular positions.
straylight PSF GI diaphragmless Giving the spatial PSF characterising stray-light contamination occurring in the ground imager, including the scrambling window.
straylight PSF spectro Giving the spatio-spectral PSF characterising stray-light contamination occurring in the spectrometer.

Table 2: Groups of the OLCI Level-1 Calibration data file

Name Description
central wavelength and bandwidth Providing the true actual characterisation of the central wavelength and bandwidth for each OLCI band at each wavelength.
inband extraterrestrial solar irradiance Giving the in-band equivalent solar irradiance (linked to the current OLCI bands characterisation) at reference sun-Earth distance (provided in the same group).
reference calibration coefficients Gathering the calibration coefficients, i.e. the overall dark offsets and gains given at a reference time (provided in the same group) for each band and each pixel.
instrument gain temporal degradation Giving the coefficients of the model describing the overall temporal degradation of the instrument.
thermoelastic model EO Providing the four quaternions for Earth Observation mode, characterising the thermoelastic deformation model defined as per-module rotation from instrument to SC frames.
thermoelastic model RC Providing the four quaternions for Calibration mode, characterising the thermoelastic deformation model defined as per-module rotation from instrument to SC frames.
sampling maps Gathering the re-sampling map identifying the valid pixels for the OLCI re-sampling process, as well as the anomalous samples map identifying all samples (i.e. radiometric pixel value provided at each band) considered to be anomalous.

Table 3 : Groups of the OLCI Level-1 Programmation data file

Name Description
microband band settings Giving the programmation of the microbands and bands for nominal and spectral calibration modes.
microband gain settings Giving the index of the VAM programmable gains used for each microband at module level.
calibration sequence Providing, for each calibration sequence, the number of frames acquired while the shutter is ON and while the diffuser is ON.